Solid 5-aminotetrazole nitrate gas generating propellant with block copolymer binder

ABSTRACT

A solid gas generating propellant based upon 5-aminotetrazole nitrate as the oxidant component and utilizing a binder matrix of a block copolymer selected from the group consisting of styrenebutadiene-styrene and styrene-isoprene-styrene.

United States Patent [191 Strecker et a1.

[ 51 Aug. 5, 1975 SOLID S-AMINOTETRAZOLE NITRATE GAS GENERATINGPROPELLANT WITH BLOCK COPOLYMER BINDER [75] Inventors: Ruediger A. H.Strecker, Oxon Hill;

Hermann S. Haiss, Indian Head, both of Md.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

22 Filed: Sept. 23, 1970 211 App1.No.:74,894

[52] US. Cl. l49/l9.9; 149/19.91; 149/92 [51] Int. Cl. .1 C06D 5/06 [58]Field of Search 149/19, 19.9, 19.91, 92

Primary Examiner-Benjamin R. Padgett Assistant ExaminerE. A. MillerAttorney, Agent, or Firm-R. S. Sciascia; .1. A. Cooke [57] ABSTRACT Asolid gas generating propellant based upon 5- aminotetrazole nitrate asthe oxidant component and utilizing a binder matrix of a block eopolymerselected from the group consisting of styrene-butadiene-styrene andstyrene-isoprene-styrene.

5 Claims, N0 Drawings SOLID S-AMINOTETRAZOLE NITRATE GAS GENERATINGPROPELLANT WITH BLOCK COPOLYMER BINDER BACKGROUND OF THE INVENTION Thisinvention relates generally to composite propellants and moreparticularly to a composite propellant especially useful as a gasgenerator.

In the past, the mainstay of gas generating composite propellants hasbeen based on ammonium nitrate as the oxidizing component. Althoughgenerally acceptable the ammonium nitrate based gas generators burn veryslowly; i.e., about 0.10 inches/sec., even with the addition of burningrate modifiers.

Consequently, large volumes of gas are not produced quickly by thesesystems and thus they are not effective for purposes where totalpressure is required immediately, for example, where the guidance of amissile is dependent upon instantaneous total pressurization.

Efforts have been made to improve the burning rates of ammonium nitrategas generators, but have not been completely successful, since theaddition of burning rate modifiers, while increasing the burning rate,cause additional problems, such as the erosion of hardware due to theformation of metal oxides not otherwise present in the system. However,a desirable characteristic of the ammonium nitrate compositions, alsodesirable for all gas generators, is its low flame temperature.

Another gas generating propellant composition which has been employed inthe past is based upon ammonium perchlorate as the oxidant. Althoughthese have higher burning rate characteristics than the ammonium nitratebased compositions, the ammonium perchlorate generators generatedeleterious corrosive gases and therefore also have limitedapplicability.

ln US. application Ser. No. 883,327 by Moy et al. filed Nov. 28, 1969, agas generating propellant composition based upon S-aminotetrazolenitrate as the oxidant was disclosed. This gas generator was found to befaster burning than the ammonium nitrate type and have a comparable lowflame temperature.

Other characteristics, such as a low burning rate slope and a rr valueof between 0.2 and 0.3, increased temperature stability, and good agingof the propellant composition, are also highly desirable properties fora solid propellant. Furthermore, the complete absence of inorganicadditives, even small amounts that are often required as curingcatalysts for the binder material or ballistic modifiers, is preferredto avoid any formation ofinorganic solids upon combustion, which areintolerable in some applications.

SUMMARY OF THE INVENTION Accordingly, it is one object of the presentinvention to provide an improved fast burning, gas generating solidpropellant composition based upon 5- aminotetrazole nitrate.

Another object of the present invention is to provide a gas generatingsolid propellant composition based upon S-aminotetrazole nitrate whichyields only noncorrosive gases upon combustion.

Still another object of this invention is to provide a gas generatingsolid propellant composition based upon S-aminotetrazole nitrate whichpossesses improved mechanical, physical and chemical characteristics.

A still further object of the instant invention is to provide a gasgenerating solid propellant composition DESCRIPTION OF THE PREFERREDEMBODIMENTS The gas generating propellant compositions of this inventionare based upon S-aminotetrazole nitrate, depicted by the structuralformula below, as the oxidizing material ll II N c NH HNO3 The oxidizingcompound of the formula is easily and conventionally prepared by theaddition of nitric acid to S-aminotetrazole.

For the purposes of this invention, the 5- aminotetrazole nitrate isincorporated in a binder matrix which is a block copolymer of styreneand butadiene or styrene and isoprene. Generally, the propellantcomposition of this invention is comprised of from about to about 87percent by weight of the compound of formula l and from about 13 toabout 25 percent by weight of the styrene-butadiene-styrene orstyrene-isoprene-styrene binder. Preferably, the present propellantcompositions are comprised of from about 84 to about 87 percent byweight of oxidant.

The styrene-butadiene-styrene and the styreneisoprene-styrene blockcopolymer binders of the pres ent invention have a molecular weightwithin the range of from about 60,000 to about 100,000 with a firstblock styrene molecular weight of from about 9,600 to about 13,600, acenter block molecular weight (butadiene or isoprene) of from about47,500 to about 69,800 and a second block styrene molecular weight offrom about 9,400 to about 14,500. The styrene content is preferablymaintained within the range of from about 28 to about 29 percent byweight and more specifically about 28.6 percent by weight. Higherstyrene contents tend to make the material too hard for propellantcomposition use.

The styrene-butadiene-styrene and styrene-isoprenestyrene blockcopolymers are rubbery materials and are commercially available asKRATON 1 102 and KRATON l 107 respectfully, manufactured by the ShellChemical Company, Emeryville, California.

The gas generating solid propellant compositions of this invention arereadily made by conventional mixing procedures. For example, the solidstyrene-butadienestyrene or styrene-isoprene-styrene copolymer isdissolved in a suitable solvent such as cyclohexane, in a ratio of, forexample, 1 part to 5 parts respectfully.

Upon the substantial solution of the copolymer, the 5- aminotetrazolenitrate and other additives such as for example anti-oxidants are addedwith mixing and under vacuum to the copolymer solution. When all thesolvent has been evaporated off, the dry mix is removed from the mixerand compression or extruded molded. The composition does not require anycuring and retains its elastic properties for an extended period oftime.

As a result of the low unsaturation (unsaturation is easily accessibleto air oxidation), which is characteristic of the copolymer binders ofthe present invention, and the absence of any inorganic additives forcuring purposes or ballistic modifying purposes, the gas generatingpropellant compositions possess excellent aging characteristics and thushave long shelf-lives. Furthermore, the excellent m, values of less than0.3, also characteristic of the present propellant compositions, arealso attributed to the copolymer binder materials employed herein.

Organic anti-oxidants and plasticizing agents also may be added in minoramounts (about 3 to percent by weight) to the propellant compositions ofthis invention for additional improved aging and mechanical properties.Specifically, some anti-oxidants which are applicable herein include2.2-methylenebis(4-methyl- 6-tertiarybutylphenol) and phenylB-naphthylamine and the like, while applicable plasticizing agentsinclude dioctyladipate, Conco oil (an aromatic hydrocarbon made by theContinental Oil Company, New York, New York,) Circolight oil (anotheraromatic hydrocarbon made by the Sun Oil Company of Phil., Pa.) and thelike. As herein before set forth the addition of inorganic materials,for example for curing purposes or ballistic modifying purposes, is notdesirable. Their pres ence, however, is not beyond the scope of thisinvention.

Having generally described the invention the following example is givenfor purposes of illustration. It will be understood that the inventionis not limited to this example, but is susceptible to differentmodifications that will be recognized by one of ordinary skill in theart.

butylphenol) The composition of Example 1 exhibited a burning rate of0.420 in./sec at 1000 psi and 77F. The popular ammonium nitrate basedgas generators generally burn only at about 0.10 inches/sec even withthe addition of burning rate modifiers which add corrosive materials tothe end combustion products. Furthermore, the composition of Example 1is further characterized by a burning rate exponent of 0.51 and a 11valve of 0.296. This constant 'rr represents the burning rate dependencyof a propellant upon changes in temperature and pressure. Thus, a lowTl' value is generally desired since the burning rate of an idealpropellant composition would be completely independent of variations intemperature and pressure. A 11 value of between 0.2 and 0.3 is thereforenoteworthy.

Furthermore, the composition of example 1 ignites at 168C and afterconstant heating at 120C it does not ignite or show any exotherm over aperiod of 24 hours, which clearly demonstrates the improved stability ofthe instant composition.

The gas generating compositions of this invention are especially useful,for instance, for actuating gas pres sure operated mechanical devices;e.g., for driving engines, electric generator motors, and turbines orfor operating pneumatic tools, and for the propulsion and guidance ofrockets or other gas escape reaction propelled devices.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent of the United States is:

1. A gas generating solid propellant composition comprising5-aminotetrazole nitrate as the oxidant and a binder matrix selectedfrom the group consisting of a styrene-butadiene-styrene block copolymerand a styrene-isoprene-styrene block copolymer.

2. The gas generating solid propellant composition of claim 1 whereinsaid styrene-butadiene-styrene and said styrene-isoprene-styrene blockcopolymers have a molecular weight within the range of from about 60,000to about 100,000 and a styrene content of from about 28 to 29 percent byweight.

3. The gas generating solid propellant composition of claim 2 whereinsaid S-aminotetrazole nitrate is present in an amount within the rangeof from about to 87 percent by weight and said block copolymer ispresent in an amount within the range of from about 13 to about 25percent.

4. The gas generating solid propellant composition of claim 3 whereinsaid block copolymer is styrenebutadiene-styrene.

5. The gas generating solid propellant composition of claim 3 whichfurther includes a minor amount of a material selected from the groupconsisting of an organic anti-oxidant, an organic plasticizing agent andmixtures

1. A GAS GENERATING SOLID PROPELLANT COMPOSITION COMPRISING5-AMINOTETRAZOLE NITRATE AS THE OXIDANT AND A BINDER MATRIX SELECTEDFROM THE GROUP CONSISTING OF A STYRENE-BUTADIENE-STYRENE BLOCK COPOLYMERAND A STYRENE-ISOPRENE-STYRENE BLOCK COPOLYMER.
 2. The gas generatingsolid propellant composition of claim 1 wherein saidstyrene-butadiene-styrene and said styrene-isoprene-styrene blockcopolymers have a molecular weight within the range of from about 60,000to about 100,000 and a styRene content of from about 28 to 29 percent byweight.
 3. The gas generating solid propellant composition of claim 2wherein said 5-aminotetrazole nitrate is present in an amount within therange of from about 75 to 87 percent by weight and said block copolymeris present in an amount within the range of from about 13 to about 25percent.
 4. The gas generating solid propellant composition of claim 3wherein said block copolymer is styrene-butadiene-styrene.
 5. The gasgenerating solid propellant composition of claim 3 which furtherincludes a minor amount of a material selected from the group consistingof an organic anti-oxidant, an organic plasticizing agent and mixturesthereof.